The medico-legal organisation said this suggested that a rise in complaints in 2009/10 was caused by changes to the NHS complaints system, rather than declining standards.

The finding comes as the GMC reported that slipping medical standards were not to blame for a 30% increase in fitness-to-practise referrals since 2004.

The MDU research found complaints were up 10% in 2009/10 but then fell by 11% in 2010/11.

It also found that although complaints increased in 2009/10, the proportion referred on to the health service ombudsman dropped by a third.

The MDU said the most common reasons for complaints were allegations of delayed or wrong diagnosis, problems with communication or issues with prescribing.

MDU medico-legal adviser Dr Jacqueline Phillips, who carried out the research, said the new NHS complaints system introduced in 2009 was likely to be behind the increase in complaints in 2009/10.

She said: 'Looking at the trends it is clear that the new complaints procedure was a factor. This meant practices were notifying us more about complaints and looking for advice on how to handle matters. The rise did not reflect a decline in medical standards.'

GP complaints

Complaints about general practice fell by 10% over the last year according to the MDU.

The drop followed a spike in complaints in the previous year.

The GMC has blamed a rise in fitness-to-practise cases on changes to the NHS complaints system.

Meanwhile, a GMC investigation showed the increase in fitness-to-practise referrals over recent years was due to improved systems of oversight and monitoring by employers.